Preliminary flight data from the deadly plane crash in Washington, D.C., shows conflicting readings about the altitudes of a passenger jet and Army helicopter that collided near Reagan National Airport and killed everyone on board the two aircraft, investigators said over the weekend.

Data from the American Airlines flight recorder showed an altitude of 325 feet, plus or minus 25 feet, when the collision happened Wednesday night, National Transportation Safety Board (NTSB) officials told reporters on Saturday. Data in the control tower, though, showed the Black Hawk helicopter at 200 feet, the maximum allowed altitude for helicopters in the area.

The roughly 100-foot altitude discrepancy in the data has yet to be explained.

Investigators are working to retrieve data from the helicopter’s back box, which is taking more time because it became waterlogged after submerging into the Potomac River, in hopes of reconciling the difference. They also said they plan to refine the tower data, which could be less reliable. 

NTSB member Todd Inman expressed frustration to reporters, noting that the board has made “several hundred” recommendations to improve aviation safety that have not been acted upon.

“You want to do something about it? Adopt the recommendation of the NTSB. You’ll save lives,” he said, adding that he has spent hours with victims’ families since the crash. “I don’t want to have to meet with those parents like that again.”

An American Airlines jet passes as family members of the victims of a midair collision between an American Airlines jet and an Army helicopter stand at the end of runway 33 near the wreckage site in the Potomac River at Ronald Reagan Washington National Airport, on Sunday, Feb. 2, in Arlington, Virginia.  (AP/Jose Luis Magana)

Families of victims visited the crash site on Sunday and divers scoured the submerged wreckage for more remains after authorities said they’ve recovered and identified 55 of the 67 people killed.

Officials said they are confident all the victims will be recovered from the chilly Potomac River.

NTSB investigators hope to have a preliminary report within 30 days, though a full investigation could take at least a year.

The Associated Press contributed to this report.